The present invention relates to the field of symbol or mark readers used to read marks (e.g., bar codes, etc.) directly on objects and more specifically to a reader that includes a motion sensor to provide enhanced reader functionality by adjusting reader operating characteristics based on sensed reader motion.
Mark or symbol reading entails the aiming of an image acquisition sensor (a CMOS camera, CCD, etc. contained within a reader) at a location on an object at which a symbol or mark has been applied, and acquiring an image of that mark. Each mark contains a set of predetermined patterns that represent an ordered group of characters or shapes that can be decoded by a processor to obtain useful information about the object (e.g. serial number, type, model, price, etc.).
During acquisition of an image of a mark, the type of illumination employed can directly affect the quality of the obtained image. For instance, where a mark is printed on a flat surface with contrasting ink or paint, high-angle “bright field” illumination often best illuminates mark features. By high-angle it is meant, generally, that light strikes the surface on which the mark is applied nearly perpendicularly (normal) or at an angle that is typically no less than about 45 degrees from perpendicular (normal) to the surface. Such illumination is subject to substantial reflection back toward im imaging sensor.
As another instance, where a mark is applied on a more irregular surface or created by etching or peening a pattern directly on a surface, the use of highly reflective bright field illumination may not be optimal. A penned/etched surface has two-dimensional properties that tend to scatter bright field illumination, thereby affecting the quality of the acquired image. In these cases, marks are often best illuminated via dark field illumination directed at the surface on which a mark is applied at a relatively low angle (e.g., approximately 45 degrees or less). Using such low-angle dark field illumination, two-dimensional surface texture is contrasted more effectively (with indents appearing as bright spots and surroundings as shadows) for better image acquisition.
In other cases, diffuse direct illumination may be optimal for imaging purposes. Such illumination is typically produced using a direct-projected light source (e.g. from LEDs) passing through a diffuser to produce a desired illumination effect.
When attempting to read and decode various types of marks on parts or components, it may be desirable to initially try one illumination type, such as bright field illumination. If the mark is not able to be read using bright field illumination, the reader may obtain an image of the mark using a second type of illumination, a third type of illumination, and so on. Some code readers have a dial or switch that must be manually toggled to change illumination modes. Manually stepping through illumination types via a switch is cumbersome and typically increases the length of time needed to successfully read a mark. Attempts to solve this problem have been made by developing a reader that sequentially steps through illumination modes while acquiring images of a mark and attempting to decode the marks in the images. This is not an optimal solution, however, as this solution may increase the length of time before a code is successfully read and decoded and additional switches/dials increase reader costs.
Similarly, depending on the type of mark to be imaged and decoded, different decoding algorithms may be employed. In some cases a reader user may be able to manually select via a dial or the like which decoding algorithm to use. In other cases a reader may be programmed to step through a series of decoding algorithms in attempts to decode a mark. As in the case of different illumination settings, switching between different decoding algorithms can be cumbersome and additional dials or switches can increase costs appreciably.
Other problems with capturing high quality images of marks via a reader are related to reader movement during imaging. To this end, if a reader is moving while an image of a mark is being captured the image can be blurred which often renders the mark in the image unable to be decoded.
In addition, reader movement can increase auto-focus time required to, as the label implies, focus a reader lens assembly on a mark to be imaged. To this end, typical readers can obtain an image of a mark suitable for decoding when the distance between the reader and the mark is anywhere within a range of distances by changing a focal length of the reader's field of view. Here, for instance, if a reader is twenty inches from a surface on which a mark has been applied and is moved toward the mark, a reader processor may be programmed to recognize that the mark is out of focus and hunt for a lens setting that brings the mark back into focus. A typical hunting process may include driving the reader lenses to juxtapositions consistent with one end of the range of focus (i.e., twenty-five inch focus) and then acquiring mark images as the focal length of the field of view is altered until the mark is again in focus. While this solution works well in some applications, one drawback is that the focus settling time can be increased appreciably when the in focus hunting process initially progresses in the wrong direction. For instance, where a reader is moved toward a mark but the reader is programmed to increase the focal length of the field of view when a mark becomes unfocused, the hunting process starts hunting in the wrong direction and settling time (i.e., focusing time) is increased. Excess focus settling time and image capturing time is bothersome.